Polyolefin such as polyethylene (PE) is synthesized by polymerizing olefin monomer such as ethylene (CH2═CH2) monomers. Because it is cheap, safe, stable to most environments and easy to be processed polyethylene polymers are useful in many applications. According to the properties polyethylene can be classified into several types, such as but, not limited to, LDPE (Low Density Polyethylene), LLDPE (Linear Low Density Polyethylene), and HDPE (High Density Polyethylene). Each type of polyethylene has different properties and characteristics.
Olefin polymerization such as ethylene polymerizations are frequently carried out in a loop reactor using ethylene monomer, liquid diluent and catalyst, optionally one or more co-monomer(s), and hydrogen. The polymerization in a loop reactor is usually performed under slurry conditions, with the produced polymer usually in a form of solid particles which are suspended in the diluent. The slurry in the reactor is circulated continuously with a pump to maintain efficient suspension of the polymer solid particles in the liquid diluent. Polymer slurry is discharged from the loop reactor by means of settling legs, which operate on a batch principle to recover the slurry. Settling in the legs is used to increase the solids concentration of the slurry finally recovered as product slurry. The product slurry is further discharged through heated flash lines to a flash tank, where most of the diluent and unreacted monomers are flashed off and recycled.
Alternatively, the product slurry may be fed to a second loop reactor serially connected to the first loop reactor wherein a second polymer fraction may be produced. Typically, when two reactors in series are employed in this manner, the resultant polymer product is a bimodal polymer product, which comprises a first polymer fraction produced in the first reactor and a second polymer fraction produced in the second reactor, and has a bimodal molecular weight distribution.
After the polymer product is collected from the reactor and the diluent residues are removed therefrom, the polymer product is dried, additives can be added and finally the polymer may be extruded and pelletized.
The inventors have found that there are numerous challenges in the production of high-yield and high-quality polyolefin such as polyethylene. They include adequate control of different reaction conditions such as temperature, pressure and flow rate. Effective design and maintenance of reactors are also required. The complex nature of the reaction slurry presents further complications. The slurry is for instance affected by the quantity and quality of ingredients or the homogeneity of the particulate polymerization catalyst dispersion which is prone to sedimentation in the slurry. Furthermore, high energy consumption needs to be avoided to lower production costs. In view of these challenges, there remains a need in the art for improved equipment to meet the rigorous requirements for high quality polyethylene production.
It is therefore the objective of the invention to provide a polyolefin polymerization reactor, in particular a slurry polymerization loop reactor for the production of polyolefin such as polyethylene, meeting high quality standards, wherein additionally energy consumption is optimized.